lO 



NATURE 



[May 6, 1S97 



kind, like that involved in the preparation of the photographic 

 cliart of the heavens, it was absolutely necessary, from the 

 magnitude of the undertaking, that a collective effort should be 

 made. In another case, that of the British Association Com- 

 niitiee on Luminous Meteors, which existed between 1848 and 

 1881, a mass of valuable work was performed (as the annual 

 ■jeports will testify) by the collection and discussion of 1 

 observations and investigation of theories. Other instances 

 might l)e adduced, but they are rather exceptional in character 

 and distinct to the ordinary sectional work of societies. 



In certain respects, it cannot be denied that the latter serve a 

 useful purpose. Many gentlemen find it an encouragement and 

 a source of interest to engage with others in combined work. 

 They are thus enabled to compare notes, and it is a satisfaction 

 to feel that a bond of association exists between them, and that 

 they are all actively employed in a similar direction. Observa- 

 tions are taken, drawings are made, and many hours are spent ] 

 at the telescope, which would never be so employed l)ut for the 

 influence of the circumstances referred to. They have the 

 pleasure of seeing their observations in print ; possibly some of 

 their drawings are also reproduced, and the consciousness of 

 having done something to merit public notice cannot fail to 

 stimulate them to further effort. But, in such cases, it must be 

 admitted that the benefit to science is inconsiderable. Very 

 little work of real value is accomplished in this way, and in 

 ■many instances the observations are not properly reduced and 

 ■utilised as they should be. It is not sufficient that results of this 

 Jcind should be simply allowed, year after year, to accumulate. 

 Many thousands of drawings and observations have been made 

 by the members of planetary sections ; but we can trace very few 

 salient facts, or additions to our knowledge, as the outcome of 

 them all. Observers, as a rule, do not probe into their subject 

 with sufficient depth, and ferret out all the details possible of 

 any particular object observed. Nor is attention always directed 

 to those points which are the most significant and suggestive. 

 It needs a man like Mr. Marth to be the really efficient director 

 of a section, to single out the really essential work to be per- 

 formed, and then to sift it with thoroughness and critical 

 accuracy. 



To beginners sectional work is often most beneficial, as it 

 affords them a useful preliminary training. But observers who 

 need and will submit to "direction," except at the outset of 

 their careers, are not generally the men who accomplish work 

 of an important and enduring kind. The aspirations of a really 

 capable man are not likely to be satisfied by the facilities offered 

 by combination with many others. It has been said, " Talent does 

 what it can, Genius does what it must." When a young observer 

 begins to feel confidence in himself, it is, perhaps, better that he 

 should strike out in a path of his own. There are some who 

 will naturally be allured by the prospects of doing original work, 

 and effecting discoveries in an independent way. They do not want 

 to triple the channels of Mars, to distinguish the hard straight 

 lines on Mercury and Venus, or to trace the zebra-leopard-like 

 aspect of the globe of Saturn. But they want to do really useful 

 work, and to rely only upon the unmistakable evidence of their 

 eyes ; in this respect, dissociating themselves from some modern 

 observers, who can but very vaguely discriminate between 

 romance and reality. 



To sum up the matter : it appears that the organised work of 

 " sections," though it unquestionably affords a stimulus to many, 

 and assists in maintaining the interest in a subject, is yet, except 

 in certain special circumstances and cases, disappointing and 

 unproductive of results which materially advance astronomy. 

 Individual and independent effort has hitherto been, and vvill 

 still continue to be, the fountain-head of the most valuable 

 work. 



In concluding, it may be mentioned that the issues of recent 

 planetary observation appear to be totally dissimilar to anything 

 previously experienced in astronomical history. No two 

 observers see alike when they examine the images of Mercury, 

 Venus, Mars, or Saturn, and the actual character of the visible 

 surface markings of these orbs is more an enigma than it was in 

 the days of Ilerschel and Schroeter. There is also a pro- 

 nounced conflict of opinion as to the utility of large and small 

 telescopes in displaying delicate features on the planets. This 

 want of unanimity amongst observers has become a serious 

 ■question to consider ; in its presence organised attempts to study 

 the planets are of little avail, since many individuals seem to 

 •display their own particular idiosyncrasies and peccadilloes, 

 greatly to the chagrin of every director of a section, who finds 

 his post no sinecure. W, F, Denning. 



NO. 1436. VOL 56] 



Shelly Glacial Deposits. 



I TEAR that the hope expressed by Prof. Bonney, somewhat 

 incongruously in its connection, in his recent review of Russell's 

 " Glaciers of North America," that " perhaps in future we shall 

 hear less of rampant ice-sheets at Gloppa and Moel Tryfan ! " is 

 not destined to be fulfilled. There will be something more to hear 

 shortly, if he care to listen, respecting that part of this ice-sheet 

 which covered the Isle of Man. This portion was distinctly of 

 the "rampant" type, as Mr. P. F. Kendall has already shown, 

 carrying up shells in one place, and boulders of Foxdale 

 granite in another, and erratics from the south of Scotland in 

 another, as a matter of every-day work — ^just as recent investiga- 

 tions have shown to be the case in regions where to-day there are 

 glaciers of other than the Alpine type, 



I am quite in agreement with Prof. Bonney when, elsewhere in 

 his review, he asks : " May not the difficulties of the subject be 

 augmented by defective knowledge ? " For this reason I may be 

 pardoned for once more dragging forward the facts which I put on 

 record some years ago respecting the shelly Basement Clay ot 

 the Yorkshire Coast. In this deposit the shells occur not only 

 scattered throughout the clay, but also in limited patches or 

 boulders of marine sand and mud, which are associated with 

 similar masses of peat and mud of fresh-water origin, and with 

 patches of shale and clay derived from the Lower Cretaceous 

 and Jurassic strata of the country farther northward with the 

 bedding still preserved and the characteristic fossils in place. 



These facts have never been impugned, but they are rarely 

 referred to by the opponents of the " rampant ice-sheets." They 

 have surely a more immediate and direct bearing upon the 

 subject than the isolated observation respecting the deposit in 

 the neighbourhood of the Malaspina Glacier on which Prof. 

 Bonney leans so wide a hope. 



If the sands and gravels accompanying this Yorkshire drift- 

 series be, as is usually held, the result of the washing-out of the 

 same material, the shelly fragments contained therein are no 

 better proof that the gravels are of marine origin than their 

 derivative Jurassic fossils are that they are of Jurassic age. 



I do not think that anyone has attempted to deny that marine 

 deposits of Glacial age may and do exist within the limits of the 

 British Islands. But what the "extreme glacialists" wish to 

 insist upon is that better evidence is required than the mere 

 presence of sporadic marine organisms to prove such origin 

 against the very strong evidence which can be adduced against 

 it in such instances as those referred to by Prof. Bonney. 



Dalby, Isle of Man, April 22. G. W. Lamplugh. 



Sieve for Primes. 



May I draw the attention of your readers to a series from 

 which the primes may be recovered ? 



The series is given below, together with the accompanying 

 primes. 



1, 4, II, 29, 76, 199. 521, 1364, 3571, 9349, &c. 

 I. 3. 5. 7- "• 13- '7- 19, &c. 



2. 



The law of formation is an+\ = 3a» - a,e-i. 



It can be proved in various ways that the «th term of 



y3)2«-i -KW4 + Tys)-"-! -l=p.q 



{w^ 



o and / = 2« — I 



13) 



where the roots arethe unreal of x^ -f 

 any odd prime. 



Is 13 a prime ? Yes ; because the 7th term (2x7 

 minus unity = 12, q- 



Is 1 5 a prime ? No ; because the 8th term less unity is not 



= 15'/- 



These are but easy numbers to test ; but the law is general. 



We have here an alternative test for primes. 



The series given above is intimately connected with the well- 

 known "continuant" series I, i, 2, 3, 5, 8, 13, &c., whose 

 law of formation is obvious. 



The connection between the two series is as follows : — 



Let a, b, be any two consecutive terms of the " continuant" 

 series. 



Then 5 a/5 + i will give the corresponding term in the former 

 series. 



There are other series which produce the primes, but the 

 above can be produced mechanically. 



